Railway signaling system



Sept. l 7, 1 940.

J. B. GRIFFITHS Er Al.

RAILWAY SIGNALING SYSTEM 2 Sheets-Sheet l Filed May 28, 1936 TTORNE Ysept. 17, 1940.,

RAILWAY SIGNALING SYSTEM Filed May 28, 1936 Fig. 2.

Fig. 3.

J. B. GRlFFrrHs 'E- AL 2,214,924

2 Sheets-Sheet 2 Patented Sept. I7, 1940 RAILWAY SIGNALING SYSTEM JohnBalmain Griffiths and Andrew Brown, London, England, assignors toInternational Standard Electric Corporation,

Application 25 Claims.

This invention relates to railway signaling systems.

ing track section in turn as that section is approached. In sucharrangements the stopping point of one tual position of sition of thebeginning of preceding train the or any part of train 1s determined notby the acthe train ahead,

but by the po'- section in which a the preceding train happens to bestanding. Further, the signals for stopping yof a train are notcontrolled dependent ing in question, nor on its own It is the object ofthe present invention on the speed at which the preceding train ismovspeed.

to provide a system of train signaling and/or control in which trainsare allowed to follow one another at the shortest intervals which areproved to be safe taking into account the distance apart of the trainsirrespective of their positions on the track and/or the speed of a trainitself and/ or the speed of the preceding train.

The main feature of the invention comprises a railway signaling systemcharacterised by a continuous electrical signaling circuit along atrack, electrical transmitting train on the track arranged along thecircuit in which the train is travelling equipment on each to beconnected to said signaling circuit to transmit information the oppositedirection to on the track, electrical receiving equipment on each'trainarranged to receive said information from the preceding train and todetermine therefrom information concerning the relative positions of thetwo trains on the track, and control ment on each train adapted controlof and/ or indicating equipto function under the receiving equipment 'togive an indication to the driver or to control the train in accordancewith its safe margin of travel as determined by the distance between thetrains irrespective of their positions on the track with respect toparticular divisions thereof.

the following description of thereof shown in which:

The invention will be clearly understood from the embodiments theaccompanying drawings, in

Fig. 1 shows a continuous signaling circuit SC connected at intervals toand also to trains T each the earthed rails ER provided with controlcircuits at the front and rear shunted between the continuous signalcircuit SC and the rails ER;

Fig. 1A shows a modied f @55 apparatus of Fig. 1.

ormof part of the New York, N. Y.

May Z8, 1938, Serial No. 210,580. In

reat Britain June l, 1937 Fig. 2 shows a modication of the signalingcircuit shown in Fig. 1, arranged for direct control of the drivingmotors of a train; while v Fig. 3 shows a train drivers speed indicator.

Referring first to Fig. l, the control circuit atthe 5 front of eachtrain comprises a source of electric potential EP and a meter M thereading of which will be influenced by the distance between the trainand the preceding train. The control circuit at the rear of eachtrain iseither a direct short circuit or an impedance connection I which may ifdesired be variable under control of a speedometer.

The continuous signal circuit is divided into sections the length ofwhich is determinedby the shortest individual vehicle or train whichmust pass over the track, under full control of the signaling equipment.

At the junction point between each pair of sections a resistance RS andrectifier RC in series are inserted into the signal circuit SC. Therectiers RC are so inserted that they pass current through the circuitSC in the direction in which trafc passes along the track. At thejunction point of each resistance and rectifier pair (or at any otherpoint in each section) a connection is made through high resistance HRto the rails ER or other dead earth. The resistances in the signalcircuit are very small compared with the high resistance shunts but arelarge compared with the resistance of the rectifiers. For instance, anordinary dry rectifier in the go direction has a resistance ofl about 3ohms. The resistance in series therewith will be about 17 ohms, whilethe shunt resistance will be about 5000 ohms. When a train passes alongthe track with no other train in front of it a circuit is formed throughthe meter, through all of the shunts HR of the signal circuit sectionsahead through the rails and the battery EP.

The resistances and the battery voltage are so chosen that in the worstcondition a certain minimum current should pass through the meter andunless this minimum currentis indicatedby the meterthetrainisnotallowedtomove. 'I'hisminimum 45 current value is determinedby the current which would be allowed to new by the shunt resistances ofa number of signal circuit sections, which cover the maximum brakingdistance of a train.

It will be appreciated that the rectiers in the sections behind thetrain prevent the shunt resistance of these sections having any effectupon the meter current.

When a train is on the track in front of the train under consideration,the meter current will per section is 300 ohms be determined by theshunt on the rear of the preceding train through which a much greatercurrent can pass than would be passed through the shunt resistances HRbetween the trains, or

by all the shunt resistances HR where no train The reading of the meterwill increase as the distance between the trains becomes less and thereading of the meter will be used to indicate to the driver the maximumsafe speed at which he can proceed or to control the speed of the trainin accordance with safe limits or automatically to prevent the traintravelling at -a speed greater than the safe speed.

If, as has been suggested previously, the shunt resistance on the rearof the preceding train is increased under control of a speedometer asthe speed of the train increases, it will be seen that the reading ofthe meter on the following train will be correspondingly decreasedenabling that train to proceed at a greater speed and run closer behindthe train in front by virtue of the fact that the preceding train isitself moving.

For the purpose of varying the resistance of the shunt placed on thesignal circuit according to the speed of the train, a series ofgovernorcontrolled contacts for cutting in and out resistance may beused.

If the driver attempts to run his train at a speed greater than thatindicated under control of the meter or if the reading of the meterreaches a certain maximum, the train will be automatically stopped byany known means.

Let us assume as an example, that the maximum braking distance of thetrains is 600 ft. and :that the signaling circuit section length is 40ft., then the number of sections corresponding to the maximum brakingdistance is 15. The signal circuit resistance of 15 sections at 20 ohmsand this corresponds roughly to fifteen 5000 ohm shunts in parallel.

The fundamental purpose of the shunt resistance is to guard against adisconnection ahead of the signal circuit. For this purpose it isnecessary for the meter to show the minimum current reading before atrain is allowed to move, whether or not there is a train on the trackahead.

It will have been noted that the resistance of is present.

each rectifier in the signal circuit is small compared with the value ofits series resistance. The reason Yfor this is to prevent small changesin the rectifier resistance eiecting the system. However,k it ispossible for the resistance of a rectifier Vin the go direction toincrease to a value of the orderof 260 or 300 ohms although this is veryunlikely as the-rectifier usually either becomes short-circuited orcompletely disconnected instead. However, if such a remote contingencyIdid arise the response of the meter, circuit or train via the shunt ofthe preceding train would be artificially increased so that thepreceding train appears much farther away than it actually is. This ofcourse is a wrong side fault. In order to take care of this, the frontcontrol circuit on each train may be connected to the signal circuit SCby a pair of sliders SL, between l which a voltmeter V is connected andwhich are spaced so as to bridge each resistance and rectifier pair RS,RC, so that the voltmeter will read 'the voltage drop across eachrectier and re- 4sistance pair in turn.

The voltmeter reading will be compared with the reading of the amperemeter M to show the actual resistance of each rectifier resistance pair.If this is high an alarm will be given and if considered necessary thetrain will be stopped.

' the meter needle The shunt connection on the rear of the train is apossible source of a wrong side fault because if it became disconnectedthe presence of the preceding train would no longer be indicated. Inorder to guard against this, several parallel shunt connections may beprovided on each train asl shown in Fig. 11A, so that if one suchconnection comes adrift, no appreciable change in the resistance of thecircuit between the two trains will arise. Provision can be made atsuitable points on the track for testing that all the par- `allelcircuits were intact.

As an alternative to the ammeter indicator, a chain of relays may beprovided, the response of which would be graded so as to operatev inturn as the signal channel resistance decreases.

Another alternative is to control the driving motor or motors of trainsdirectly by the signal channel resistance. Such an arrangement is shownin Fig. 2, and is a modication of the D. C. system described above. Asource of direct current, CS, is connected between a wheel rail WR and alive rail LR. Between WR and the mid-points of the resistance-rectifierpairs RS, RC in the signal wire SW, the shunt circuits HR are connected.

The drivingfmotor MOis also connected between WR and SW by wheel WH andslider SLC in series with normally open contacts Zd and the relay LDcontrolling said contacts. Between Zd and LD is connected a current feedcircuit via resistance FR and slider SLR.

For a train to start, a circuit for operating LD is completed via SLC,HR, CS, LR, SLR and FR. LD will only operate if the signal channel is inorder, thereby closing contacts Zd to complete the circuit for motor MO.A shunt on motor MO is maintained via. LD, SLC, SW shunt circuits HR andWR, so that the excitation of the motor decreases as the resistance ofthe shunt decreases. In this way the speed of the trains' may beautomatically controlled. Y

Automatic train speed control could of course be obtained by theprovision of an intermediate control relaying means between, an ammeteror relay chain and a motor shunt or other automatic control means. Forinstance, the meter could be provided with power operated means toyoperate one of a number of control circuit pairs via according to theposition of the needle, the contacts being used to control a motor shuntor other motor control device.

Fig. 3 shows a train drivers speed indicator designed to give himdetailed speed information and a very simple maximum speed check device.

The indicator comprises two red indicator segplied full braking power.The segment S is controlled by the speedometer and yrotatesanticlockwise as the speed increases. The pointer HLP on H indicates ona scale the maximum per- `missible speed while pointer SP on S indicatesthe actual speed of the train.

As the trainy speed approaches the maximum allowable speed, 'the visiblegreerr background G decreases in size and is blotted out completely whenthe train reaches the kmaximum speed. The indicator is arranged 'to`operate contacts SW, shunt circuits C and when the vgreen disappears tocause automatic application of the brakes. The main features of theindicator are the variable indication of the margin of speed and theautomatic brake control.

Signaling between trains may be performed by measuring the resistance ofa direct current circuit via the intervening signal circuit between twotrains, or the resistance or phase angle of an alternating currentcircuit.

Inductive connections between the trains and the signal circuit may beused.

Instead of using a constant potential to measure variable lineresistance or impedance, it is possible for each signal section toinsert additional D. C. or A. C. voltage in the circuit between twotrains so that the voltage is a measure of the degree of freedom ahead.

i It is sometimes necessary to apply either temporary or permanent speedrestrictions on a portion of a track, for instance a newly-laid portionor a sharp curve. A condition can then be connected to the signalchannel near the beginning of the section in question, which will causea train to slow down to the required speed before entering the section.If the section is long, it may be necessary to apply two or more suchconditions spaced along the section to be restricted. In the case of theD. C. system, this condition could be a resistance leak by additionalresistance units HR.

If it is desired to pass locomotives or trolleys shorter in length thanthe signal channel sections along the track, they can be provided withequipment for short-circuiting the channel for instance, to safeguardtheir rear, but will not be provided with detector equipment for testingthe condition of the portion of the signal channel ahead.

An important facility offered by the system is the possibility ofgoverning the approach speed and distance of trains according to thegradient of the track. This :facility is obtained in the D. C. systemfor example, by varying the values of the shunt resistances across thesignal channel to allow relatively greater speeds and shorter spacingson up-gradients than on level track sections, and on level sections thanon down-gradients.

What is claimed is:

1. A railway signaling system comprising a continuous electricalsignaling circuit along a track including as a part thereof the trackrails, means in said circuit for conducting current in one directiononly along a portion of said circuit, electrical receiving means and acurrent source on each train connected to said circuit, a transmissionmodifying means on each train connected to said circuit for modifyingthe current f path for the current source on a following train,

said receiving means on each train for receiving current from. thecurrent source of a preceding train, and responsive to its positionrelative to the transmission modifying means on said preceding train forindicating the distance between said trains in accordance with the safemargin of travelfunder control of said current'source.

2. A railway signaling system as claimed in claim 1, wherein means isprovided to control said transmission modifying means according to thespeed of travel of the train on which it is mounted and said receivingequipment is arranged to control the indicating equipment in accordancewith the combined distance from the preceding train and the speed ofmovement of the preceding train.

3. A railway signaling system as claimed in claim 1, characterised inthis that said indicating and control equipment includes a maximum safespeed indicator for the driver.

4. A railway signaling system as claimed in claim 1, characterised inthis that said indicating and control equipment includes a maximum safespeed indicator, and automatic braking equipment brought into operationin response to speeds exceeding said maximum safe speed.

5. A railway signaling system as claimed in claim 1, characterised inthis that the continuous signaling circuit comprises a rst continuouselectric conductor formed by short conductor sections each adjacent paircomprising a recti` iier, a second continuous electrical conductorparallel to said interconnected conductor sections, and a highresistance bridge per section of the first conductor between the firstand second conductors, that said transmission modifying means on eachtrain comprises a movable bridge connection between the two conductorsof the con tinuousI signaling circuit, and that the receiving equipmentis also bridged across the conductors.

6. A railway signaling system characterised by a continuous signalingcircuit comprising a first continuous electric conductor formed by shortconductor sections each adjacent pair of which is connected by aresistance and rectier in series said rectiers being poled to transmitcurrent .in one direction only along said conductor, a secondcontinuousl electrical conductor parallel to said interconnectedconductor sections, and a high resistance bridge per section of thefirst conductor between the nrst and second conductors, the resistancesin the iirst conductor being small compared with the bridge resistances,transmission modifying equipment on the rear of each train comprising amovable bridge connection between the two conductors of the con tinuoussignaling circuit and equipment on the front of each train also bridgedacross the conductors of the signaling circuit comprising a source ofdirect current potential and an indicator, the rectiiiers in the rstconductor of the continuous signaling circuit being poled to allowcurrent to flow therein from the direct potential source of one trainover the transmission modifying equipment of the preceding train and tothe indicating means of said one train.

7. A railway signaling lsystem as claimed in claim 6, characterised inthis that saidgsecond conductor is formed by the running rails'.

8. A railway signaling system as claimed in claim 6, characterised inthis, that each high resistance bridge on the continuous signalingcircuit is connected to the rst conductor at the junction between aresistance and rectifier interconnecting a pair of conductor sections.

9. A railway signaling system as claimed in claim 1, characterised inthis that the receiving means is provided with means responsive to thereceived currents to automatically control the speed of the train.

10. A railway signaling system as claimed in claim 6 characterised inthis that each section resistance of a direct current circuit, betweentwo trains.

12. A railway signaling system as claimed in claim 6, characterised inthis that the indicating equipment of each train is connected to thefirst conductor by two sliders spaced sufliciently to bridge eachrectier in the rst conductor in turn, and a voltmeter connected betweensaid sliders by means of which the condition of the rectiers may bedetermined,

13. A railway signaling system as claimed in claim 6, characterised inthis that each transmission modifying equipment comprises a plurality ofparallel bridge connections.

14. A railway signaling system as claimed in n claim 6, characterised bya variable resistance in said bridge connection of each transmissionmodifying equipment and means for varying said resistance in accordancewith the speed of the train.

15. A railway signaling system as ciaimed in claim 1, characterised inthis that the signaling circuit is divided into sections each of whichis e shorter than the distance between transmitting and receivingequipment on the shortest train which is to pass over the track underfull control of the system.

16. A railway signaling system as claimed in claim 6 characterised inthis that the signaling circuit is divided into sections each of whichis shorter than the distance between transmitting and receivingequipment on the shortest train which is to pass over the track underfull control of the system, and in this that a rolling stock unit orgroup of units which is' to pass over said track and which is shorterthan a signaling circuit section is provided with transmitting equipmentonly.

17. A railway signaling system as claimed in claim 1 characterised inthis that the electrical characteristics of the signaling circuit varyfrom portion to portion of said circuit in accordance with the gradientof the track for instance.

18. A railway signaling system as claimed in rclaim 6 characterised inthis, that the indicating equipment on a train comprises a chain ofrelays graded to operate in turn as the distance between trainsdecreases.

19. A railway signaling system as claimed in claim 1 characterised inthis that means are provided to control the driving motor or motors' ofan electric train directly by the variable re` sistance of the signalingcircuit between said train and the preceding train.

20. A railway signaling system as claimed in claim 6 characterised by anelectric driving motor for each train forming part of an indicatorbridge circuit, a live rail together with the second conductor of thesignaling circuit forming the driving current feed circuit and a feedconnection from a point on the indicator bridge circuit of each trainbetween the first signaling circuit conductor and the motor to a shoecontacting with the live rail.

2l. A railway signaling system as claimed in claim 6, characterised byan electric driving motor for each train forming part of the receivingbridge circuit, a live rail which together with kthe second conductor ofthe signaling circuit forming the driving current feed circuit and afeed connection from` a point on the receiving bridge circuit of eachtrain between the rst signaling circuit conductor and the motor to ashoe contacting with the live rail, a relay connected in the indicatingequipment of each train between the rst conductor of the signalingcircuit and said feed connection, and contacts controlled by said relay,closed when thev relay is energised, in the motor feed circuit portionof indicator equipment bridge.

22. A railway signaling system as claimed in claim 1, characterised byan indicator on each train comprising two the receiving equipment toindicate maximum permissible speed, the other controlled by aspeedometer to indicate actual speed.

23. A railway signaling system( as claimed in pointers, one controlledby claim 6, characterisedby an indicator on'each train comprising twopointers', one controlled by said indicating equipment to indicatemaximum permissible speed, the other controlled by a speedometer toindicate actual speed, said pointers of the indicators carrying screenswhich approach one another when the margin between train speed andpermissible speed decreases, and by doing so decrease the amount of abackground visible between said screens, so lthat the safety marginindication is reduced to an arbitrary minimum when the train istravelling at the maximum permissible speed.

24. A railway signaling system as claimed in claim 6, characterised byan indicator on each train comprising two pointers, one controlled bysaid receiving equipment to indicate maximumi permissible speed, theother controlled by a speedometer to indicate actual speed, saidpointers of the indicators carrying screens which approach one anotherwhen the margin between train speed and permissible speed decreases, andby doing so decrease the amount of a background visible between saidscreens, so that the safety margin indication is reduced to anarbirninimum when the train is travelling at the maximum permissiblespeed, and contacts on said indicator closed when the maximum:permissible speed is reached and which cause application of the trainbrakes.

25. A railway signaling system as claimed in claim 6, characterised byan indicator on each actual speed, pointers of the indicators carryingscreens which approach one another when the margin between train speedand permissible speed decreases, and by doing so decrease the amount ofa background visible between said screens, so that the safety marginindication is reduced to an arbitrary minimum when the train istravelling at the maximum permissible speed, and means, controlled bythe indicating equipment to indicate that the signal circuit is out oforder, comprising a section of the background which is of differentcolor displayed independently of the position of the screen whichindicates actual speed.

JOHN BALMAIN GRIFFI'IHS.

ANDREW BROWN.

